Over-The-Horizon Radar. A short overview with focus on surface-wave OTH

The technology for radar with a range beyond the horizon is not new and has been studied in the past. Surveillance systems of this type are known as Over-The-Horizon radar (OTH radar). A literature survey in this field has been conducted and shows a lot of activities during the last decades. Focus has been on publications addressing surfacewave OTH which, from a Swedish perspective, is considered to be more interesting from an operational, economical and practical point of view when compared to skywave OTH implementations. OTH systems aimed for surface current measurements have been installed along the shorelines in several countries and shown to have a detection capability with limited performance against vessels. The theoretical understanding has increased, as has the practical possibility of using new waveforms and advanced signal processing to circumvent several of the traditional limitations. This has led to new concept ideas with potentially better performance. These need to be verified by practical experiments in Swedish territorial waters. A first attempt was initiated along the Swedish west coast during the fall of 2014 by SMHI (Swedish Meteorological and Hydrological Institute). Continuous measurements of surface currents will be made during six months using two deployed radar systems and trials with moving vessels are also planned. Some preliminary calculations have been made for the reduction in maximum range expected for a similar system configuration in the southern part of the Baltic where the salinity is lower.